Average nutrient concentration, and growth characteristics of bacteria during USCGC Healy cruises in 2002 and 2004

Standing stocks and production rates for phytoplankton and heterotrophic bacteria were examined during four expeditions in the western Arctic Ocean (Chukchi Sea and Canada Basin) in the spring and summer of 2002 and 2004. Rates of primary production (PP) and bacterial production (BP) were higher in the summer than in spring and in shelf waters than in the basin. Most surprisingly, PP was 3-fold higher in 2004 than in 2002; ice-corrected rates were 1581 and 458 mg C/m**2/d respectively, for the entire region. The difference between years was mainly due to low ice coverage in the summer of 2004. The spatial and temporal variation in PP led to comparable variation in BP. Although temperature explained as much variability in BP as did PP or phytoplankton biomass, there was no relationship between temperature and bacterial growth rates above about 0°C. The average ratio of BP to PP was 0.06 and 0.79 when ice-corrected PP rates were greater than and less than 100 mg C/m**2/d, respectively; the overall average was 0.34. Bacteria accounted for a highly variable fraction of total respiration, from 3% to over 60% with a mean of 25%. Likewise, the fraction of PP consumed by bacterial respiration, when calculated from growth efficiency (average of 6.9%) and BP estimates, varied greatly over time and space (7% to >500%). The apparent uncoupling between respiration and PP has several implications for carbon export and storage in the western Arctic Ocean.2002年与2004年的春夏两季，研究团队于北冰洋西部海域（楚科奇海与加拿大海盆）开展四次科考航次，对浮游植物与异养细菌的现存量（standing stocks）及生产速率展开观测分析。初级生产（Primary Production，PP）与细菌生产（Bacterial Production，BP）速率在夏季显著高于春季，且陆架水域的速率高于海盆区域。尤为值得关注的是，2004年的初级生产速率较2002年高出3倍；全区域经海冰校正后的平均速率分别为1581与458 mg C/m²/d。年度间的速率差异主要源于2004年夏季海冰覆盖率偏低。初级生产的时空波动，使得细菌生产也呈现出与之相当的变异性。尽管温度对细菌生产变异性的解释能力与初级生产或浮游植物生物量相当，但当水温高于约0℃时，温度与细菌生长速率之间并无显著关联。当经海冰校正的初级生产速率高于与低于100 mg C/m²/d时，细菌生产与初级生产的平均比值分别为0.06与0.79，整体平均比值为0.34。细菌在总呼吸作用中的占比波动幅度极大，介于3%至60%以上，均值为25%。同理，基于生长效率（平均为6.9%）与细菌生产估算值计算得到的、由细菌呼吸作用消耗的初级生产占比，在时空维度上同样存在显著差异（7%至500%以上）。呼吸作用与初级生产之间的表观解耦现象，对北冰洋西部海域的碳输出与碳封存过程具有多重启示意义。